Look, I'm a peacenik, a former beatnik, a former hippie, nearly a pacifist, I get tweets from the f'n Dahlai Lama on my cell phone. I don't like guns, I don't like wars, and would say I have opposed almost every U.S. military action since WWII.
But you can only push people so far, and even the most pacifistic will react violently. We watched live on TV as thousands of people were murdered by this scumbag's evil plan. Grandmothers, childrens, wives, husbands, all loved ones of many good people perished right before our eyes.
I personally could go out and kill this fiend. I would have to go to a gun store and learn which end of the weapon to use, but if that is a war crime, I would have to go on trial. And I don't think many Americans would feel any differently, nor would the majority of people worldwide.